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The lawyer for a double-murder accused says his client was psychologically manipulated by a "relentless and highly-controlling" undercover police operation.

Kamal Gyanendra Reddy, 42, is on trial before the High Court at Auckland accused of murdering Pakeeza Yusuf, 33, and her 3-year-old daughter Juwairiyah "Jojo" Kalim .

The pair were found buried under the Takapuna overbridge in October 2014 after Reddy made admissions to undercover officers that he had strangled the adult victim then smothered her child with a pillow at the end of 2006 or early 2007.

Defence counsel Jonathan Krebs accepted a so-called confession was powerful evidence for the Crown but he urged the jury, in his closing address, to consider the situation in which his client made the statement.

"The context is everything."

Reddy's admissions came at the end of an extensive six-month secret investigation during which undercover cops gained the defendant's trust.

"What if the context surrounding that confession meant the confessor thought there would be no consequences adverse to him? What if the confessor thought that any problem... would go away? What if they thought making a false confession would bring benefits to them?" Mr Krebs asked.

He said the operation used "used trickery, deceit and psychological manipulation" to the point where his client believed admitting the murders would actually help him.

Mr Krebs said his client was put under immense pressure to admit to the murders and even likened the acting by officers as "worthy of Liam Neeson in the movie Taken".

The details of the scenarios Reddy was put through are suppressed so as not to jeopardise other such operations.

While in the witness box this week, Reddy said the real killer was a part-Indian man called James who was in a relationship with Ms Yusuf at the time.

He told the court James approached him after committing the murders and the only role he played was to suggest a location to bury the bodies.

Reddy was assisted in that task by his uncle Bal Naidu, who gave evidence of the defendant coming to his Papatoetoe home in the middle of the night, admitting he had killed the pair and that they were in the boot of his Subaru.

Mr Krebs urged the jury to treat the evidence with caution since Mr Naidu had confessed to his role in showing Reddy the North Shore and subsequently sentenced to home detention last year.

A two and a half hour interview condensed into less than five pages of police notes, rather than questioning being video recorded, might make the jury wonder what was discussed, Mr Krebs said.

Crown prosecutor Natalie Walker said there were details in Reddy's confession that could only have been known by the killer.

She pointed to his description of the victims being laid side by side in a muddy grave and covered in stones.

However, Mr Krebs said there were inconsistencies in how the bodies were found when compared to how Reddy describe them.

The defendant told police Ms Yusuf had been wearing a jumper but she was found in a T-shirt, while Jojo was wearing tights and perhaps not a nightie as Reddy had said.

The Crown said the pair were killed while they slept in their Howick flat but Mr Krebs suggested the clothes they were found in seemed much more like day wear.

"The confessions are not reliable," he concluded.

Justice Raynor Asher will sum up the case this afternoon before the jury begins deliberations.